I am currently on episode 25 of Death Note, and I’m unsure about why I should continue. This is why I agree with you.
The same goes for SAO. After watching the first season, I don’t see any reason to continue. It has a perfectly fine plot, which, in my opinion, doesn’t need any extension.
However, I’m still happy for fans of both of these shows that they got more. At the moment, I’m content with not continuing either. They may not have a proper ending for me, but it’s not like I’m unsatisfied.
I don’t hate it ¯_(ツ)_/¯ It is not the best thing I ever watched, but I also don’t regret continue watching it and I will probably continue doing so.